(1) Field of the Invention
This invention relates to a mechanism for actuating the valves of an internal combustion engine, and more particularly relates to a mechanism for varying the timing of the valves of an internal combustion engine in order to optimize the efficiency of the engine at different operating load and speed conditions.
(2) Description of the Prior Art
Various types of mechanisms and devices have been heretofore advanced for varying the timing of the intake and/or exhaust valves of internal combustion engines in order to improve the efficiency and performance of the engine when operating at different speeds and loads. One such mechanism is disclosed and claimed in my prior U.S. Pat. No. 4,205,634, granted June 3, 1980. This mechanism includes a rotatable camshaft having a plurality of conjugate or multi-element cam assemblies thereon, there being one assembly for at least each intake valve of the engine. Each conjugate cam assembly included an identical pair of axially spaced cams and a smaller and differently contoured cam positioned between the two axially spaced cams. The axially spaced cams were contoured to provide a timing for the associated valve such as would optimize the performance of the engine throughout one operating load and speed range, and the smaller cam was contoured to provide a different timing for the valve such as would optimize the performance of the engine throughout another operating load and speed range.
An elongated finger follower was positioned between each axially spaced pair of cams and was shiftable between a retracted position wherein the follower was out of contact with the central cam for all rotated positions thereof. Consequently, the timing of each valve was controlled solely by the axially spaced pair of cams. Each finger was also shiftable to an extended position wherein the finger engaged the central cam of its assembly throughout at least a portion of or for a complete revolution of the cam assembly. Consequently, the timing of the valve was controlled either by the axially spaced cams, or in part by the axially spaced pair of cams and the central cam, or solely by the central cam. Thus, different valve timings could be obtained for optimizing the power and efficiency of the engine for different speed and load conditions by extending or retracting each of the elongated fingers of the mechanism.
While the variable valve timing mechanism disclosed in my prior patent is capable of improving the efficiency and power output of an engine in which it is installed, during certain intermediate modes of operation and under certain conditions, undesirable acceleration rates of some of the components of the valve train could occur.
In addition to the variable valve timing mechanism disclosed in my prior patent, a control means for internal combustion engines is disclosed in the U.S. Pat. No. 2,260,983 to Walker, wherein the timing and lift of the valves of an engine could be changed by shifting a pair of parallel levers or followers in opposite directions to different positions between the tappets and lobes of multi-lobed cams. Each of the shiftable levers of the Walker control means included an operating surface having a planar surface portion and an adjoining, curved surface portion. The respective surface portions provided different points of opening and closing for the associated valves in accordance with the positions of the levers in relation to the lobes of the cams. The control means of the Walker patent was complicated and costly in that it required precise, simultaneous movement, in opposite directions, of the shiftable levers to effect a change in valve timing and could result in excessive rates of acceleration of the components of the structure due to the discontinuities at the junctions of the planar and curved surface portions of the levers.
A mechanism for varying the timing of the valves of an interal combustion engine is also disclosed in the U.S. Pat. No. 2,934,052 to Longenecker, wherein an arcuately-shaped cam follower was positioned between a pair of cams for each intake and exhaust valve of the engine, the followers being operable to transmit movement from one or the other of the associated cams to the associated valve. Each follower was provided with recesses at longitudinally spaced positions therealong to accommodate passage of the lobes of one or the other of the cams without transmitting movement to the valve. In addition, each follower was arcuately shiftable to permit selective operation of one or the other of the cams for each valve. The Longenecker mechanism was incapable of providing a valve timing other than could be obtained from the two cams, was complicated, and likewise could result in excessive rates of acceleration of the components of the mechanism.
A mechanism for changing the timing and lift of the valves of an internal combustion engine is disclosed in the U.S. Pat. No. 3,413,965 to Gavasso, which utilized a pivotally mounted lever interposed between the valve actuating rocker arm and an eccentric or cam on a rotatable shaft such that the point of engagement of the lever with the upper surface of the rocker arm could be varied during rocking movement thereof. Such rocking movement was accomplished by a push rod, one end of which engaged the rocker arm and the other end of which rode on a cam on the camshaft of the engine. The valve timing adjusting mechanism disclosed in the Gavasso patent was complex in construction, noisy, resulted in a slower than desirable valve action, and was susceptible to the development of excessive lash in the components thereof.